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Abstract
Seven years of experience operating upper-room ultraviolet irradiation systems (UVGI) in 14 homeless shelters in six cities has taught the Tuberculosis Ultraviolet Shelter Study (TUSS) many valuable lessons about maintaining uninterrupted UV services and acceptable intervals between UV lamp changes and cleaning activities. One year (9,000 hours) of continuous illumination resulted in a reduction in UVC output of the two types of low pressure mercury lamps by 17 percent for the quartz, instant start tubular lamp and 25 percent for the preheat compact lamps. The reduction over time was due to metal accumulations on the inside of the glass plus increasing opaqueness (solarization) due to UV irradiation. Cleaning frequency was found to be highly site-specific. Lamp failure was infrequent and within the manufacturers' stated life period.